1. Field of Invention
This invention pertains to the technical field of adhesive tapes. More particularly, it relates to an adhesive tape with the use of a biodegradable resin film.
2. Description of Related Art
There have been widely employed adhesive tapes comprising a base film and an adhesive layer formed thereon. When a separate film is to be bonded onto the adhesive layer, the adhesive force between the base film and the adhesive layer should exceed the adhesive force between the separate film and the adhesive layer. Therefore, techniques have been developed to improve the adhesive force between the base film and the adhesive layer by, for example, roughing the surface of the base film by sandblasting, etc., subjecting the base film to surface treatments such as corona discharge, or forming a primer layer on the base film and then forming an adhesive layer on the surface of the primer layer.
Various materials such as paper, plastic films, and metal foils are used for base films. When adhesive tapes are disposed by incineration, base films made of plastics sometimes evolve toxic gases, thus causing environmental pollution. When dumped into the ground, on the other hand, it is feared that plastic base films are not degraded and thus damage the ecological systems.
In recent years, therefore, attempts have been vigorously made to develop adhesive tapes with the use of biodegradable materials as the base or the separate film which are spontaneously degraded by microorganisms after disposal. Among these adhesive types, those wherein polylactic acid films are used as the base film have attracted public attention because of the excellent adhesiveness and strength thereof.
With respect to surface treatments to be carried out to elevate the adhesive strength to a polylactic acid film, corona discharge costs a great deal for the plant and equipment but can establish only insufficient effects, while the formation of an undercoating layer, such as a primer layer, etc., might deteriorate the biodegradability.
On the other hand, a cellophane tape comprising a base film made of cellophane, which is poor in moisture resistance, is usually produced in the following manner. Namely, a saran resin is applied to the both faces of the cellophane base to thereby improve the moisture resistance and then a primer layer is formed on one of the faces. Next, an adhesive layer is formed on the surface of the primer layer and the other face is subjected to a separation treatment followed by winding around, thereby giving a single-sided adhesive tape roll.
As discussed above, complicated processes are needed to produce single-sided tapes in the prior art.
An object of the present invention, which has been completed to solve the above-mentioned problems encountering in the prior art, is to provide a biodegradable adhesive tape. Another object of the present invention is to provide a technique for imparting opaque, colored and long-life characteristics to an adhesive tape without deteriorating the biodegradability thereof.
The present invention provides an adhesive tape comprising a biodegradable base film and an adhesive layer formed on the base film, wherein the surface of the base film is rubbed by a means of rubbing and then the adhesive layer is formed on the thus rubbed surface.
The present invention further provides an adhesive tape comprising a biodegradable base film, a primer layer formed on the base film and an adhesive layer further formed on the primer layer, wherein the surface of the base film is rubbed by a means of rubbing and then the primer layer is formed on the thus rubbed surface.
In these adhesive tapes according to the present invention, the base film has a polylactic acid film the surface of which can be rubbed as described above.
In this case, a biaxially oriented polylactic acid film may be used as the polylactic acid film.
In the adhesive tape according to the present invention, on the other hand, the base film may be provided with a Bionolle film the surface of which can be rubbed as described above.
In the adhesive tapes of the present invention as described above, the adhesive layer may contain as the main component an adhesive which does not deteriorate the biodegradability of the base film.
In this case, a natural rubber can be used as the adhesive.
In the adhesive tape of the present invention as described above, the adhesive layer may contain an opaque filler which does not deteriorate the biodegradability of the base film.
In this case, as the opaque filler, a water-insoluble one can be used.
In the adhesive tape of the present invention as described above, the adhesive layer may contain a coloring agent which does not deteriorate the biodegradability of the base film.
In this case, as the coloring agent, an oil-soluble one can be used.
When the adhesive layer of the adhesive tape as described above contains a polyisoprene rubber, the adhesive layer can contain a phenolic age resistor.
In the adhesive tape as described above, a separate film may be bonded onto the adhesive layer.
In this case, as the separate film, a biodegradable one may be used.
In this case, the separate film comprises a polyvinyl alcohol film.
In the case of an adhesive tape comprising a base film made of a resin, either biodegradable or not, and a rubbery adhesive layer formed on the surface of the base film, on the other hand, the surface of the base film may be rubbed by a means of rubbing and then the rubbery adhesive layer can be formed on the thus rubbed surface.
As a non-biodegradable base film, a polyester film or a polyimide film may be used.
In a process for producing an adhesive tape comprising feeding a base film shaped in a tape in the longitudinal direction, and applying a solution of ingredients of adhesive layer onto the surface of the base film to thereby form an adhesive layer, the surface of the base film is rubbed by a means of rubbing prior to the application of the solution of ingredients of adhesive layer in the present invention.
In this case, the solution of ingredients for adhesive layer may contain an organic compound as a solvent.
In a process for producing an adhesive tape comprising feeding a base film shaped in a tape in the longitudinal direction, applying solution of ingredients of primer layer onto the surface of the base film to thereby form a primer layer and then applying solution of ingredients of adhesive layer onto the surface of the primer layer to thereby form an adhesive layer, the surface of the base film is rubbed by a means of rubbing prior to the application of the solution of ingredients of primer layer in the present invention.
In this case, the solution of ingredients of primer layer may contain an organic compound as a solvent and the solution of ingredients of adhesive layer may contain water as a solvent.
The present invention has the constitution as described above and provides an adhesive tape comprising a biodegradable base film made of a polylactic acid film or a BIONOLLE film and an adhesive layer formed on the base film. The adhesive layer is formed by rubbing the surface of the base film desired times by a means for rubbing and then applying solution of ingredients of adhesive layer directly thereon followed by drying. Alternatively, a primer layer is formed on the rubbed surface and then the adhesive layer is formed on the surface of the primer layer.
In the prior art, only a poor adhesive force is established between a biodegradable film and an adhesive layer. When the surface of a base film is rubbed, the adhesive force between the base film and the adhesive layer can be elevated and thus a biodegradable adhesive tape can be obtained.
An adhesive tape which is biodegradable as a whole can be obtained by using a biodegradable adhesive component (for example, a natural rubber) in the adhesive layer and a biodegradable film (for example, a polyvinyl alcohol film) as the separate film.
When fillers or coloring agents are added to the adhesive layer for opacifying, it is preferable to use additives which do not deteriorate the biodegradability of the adhesive layer.
When solution of ingredients of adhesive layer contains water as a solvent, the adhesive force cannot be elevated merely by rubbing the surface of the base film. When a primer layer is formed by applying solution of ingredients of primer layer containing an organic compound as a solvent on the rubbed surface of the base film, the adhesive force between the base film and the primer layer is elevated. Thus, an adhesive tape can be obtained by forming an adhesive layer on the surface of the primer layer. Since the primer layer may be thinner than the adhesive layer, the amount of the organic solvent required in producing the adhesive tape can be thus reduced.